Method of sweetening hydrocarbon oils



Patented Dec. 3, 1935 UNITED STATES 2,022,942 METHOD OF SWEETENING HYDRO- CARBON OILS Walter A. Schulze and Lovell V. Chaney, Bartlesville, Okla, assignors to Phillips Petroleum Company, Bartlesville, Okla, a corporation of Delaware No Drawing. Application December 2, 1933, Serial No. 700,701

8 Claims. (Cl. 196-29) This invention relates to a method of treating hydrocarbon fluids and the like, with particular reference to sweetening petroleum hydrocarbon oils.

One object of this invention is to convert certain malodorous sulfur compounds occurring in petroleum hydrocarbon mixtures into less obnoxious substances.

A further and most important object is to accomplish said conversion of these obnoxious sulfur compounds by means of alkali and alkaline earth hypochlorite solutions and utilize a portion of the hypochlorite-treated product as a means of converting a still further quantity of these sulfur compounds into less obnoxious ones, obtaining a sweetened product substantially free from corrosive substances and substantially more stable in sunlight, particularly in the presence of hydrocarbons having been subjected to pyrolysis.

The term sweetening is usually applied to processes involving the conversion of malodorous mercaptans, occurring in petroleum hydrocarbon mixtures, into less odorous substances. Since one of the accepted characteristics of a good motor fuel is its freedom from obnoxious odors, substances responsible for such odors are accordingly usually either completely removed from the petroleum oil being processed at some stage of the refining process, or are converted by some means to more agreeable-smelling substances. The latter method is employed in many cases and the conversion is accomplished by some oxidizing agent, mercaptans occurring in the petroleum hydrocarbon mixture being converted principally to disulfides. The extent of this conversion is usually determined by the well-known doctor, or sodium plumbite, test.

In sweetening petroleum hydrocarbon fluids with alkali or alkaline earth hypochlorite solutions, the sweetened fluid is, in many instances, corrosive to the well-known copper strip corrosion test and becomes much darker in color when exposed to sunlight, particularly if the sweetened product has been produced by cracking, or pyrolysis, or is mixed with a petroleum oil which has been subjected to cracking conditions.

We have discovered that these hypochloritesweetened hydrocarbon fluids possess certain oxidizing properties and that we can utilize them as active sweetening agents in sweetening sour hydrocarbon fluids, thereby effecting a considerable saving in sweetening expense. We have further discovered that the composite mixture of hydrocarbon fluids sweetened by this means is less corrosive to the copper strip and is more stable to sunlight.

We have, by way of example, intimately mixed one volume of a sodium hypochlorite-sweetened solution of tertiary butyl mercaptan in sulfurfree naphtha (0.021 per cent by weight mercaptan sulfur in the solution) with one volume of the same mercaptan-containing naphtha solution before sweetening, and obtained a mixture sweet to the doctor test. Since the mercaptan content of the composite after mixing would be approximately 0.01 per cent sulfur as mercaptan sulfur and the doctor test is sensitive to approximately 0.0002 per cent tertiary butyl mercaptan sulfur, a fully sweetened product could not have been the result of dilution such that the amount of mercaptan sulfur in the composite was out of range of detection by the doctor test. This example shows that the compound formed during the treatment of tertiary butyl mercaptan in naphtha solution with hypochlorite solution will oxidize approximately an equivalent quantity of mercaptan sulfur.

It is believed that the reaction which takes place between the tertiary butyl mercaptan and sodium hypochlorite solution is expressed as follows:

The -t-butyl sulfur chloride belongs to the general class of compounds called alkyl sulfur chlorides. The chlorine in these compounds has a valence of +1, just as in the sodium hypochlorite. and this accounts for the fact that these compounds have oxidizing properties.

As another example, 4.0 volumes of hypochlorite-sweetened tertiary butyl mercaptan stock (which had contained 0.021 per cent mercaptan sulfur) were intimately mixed with 30 volumes of a highly cracked naphtha containing 0.03 per cent sulfur as mercaptans. The composite was sweet to the doctor test.

As a still further example, 2.2 volumes of -a sodium hypochlorite-sweetened West Texas natural gasoline were mixed with 1 volume of the same gasoline before sweetening and we obtained a doctor-sweet mixture. Before sweetening, the natural gasoline contained 0.02 per cent by weight of mercaptan sulfur.

In these examples the sodium hypochlorite solution employed for sweetening comprised 30 grams of sodium hypochlorite and 5 grams of excess sodium hydroxide per liter.

In addition to the saving in sweetening cost by utilizing portions of hypochlorite-sweetened naphthas and the like to sweeten sour portions of the same, the sweet composites were substantially less corrosiveto the copper strip and, when blended with a highly cracked gasoline, were substantially more stable to sunlight than the hypochlorite-sweetened naphthas before blending with sour products.

In operating our method of sweetening petroleum hydrocarbon fluids, we sweeten a portion of the sour hydrocarbon fluid with a sodium hypochlorite solution comprising sodium hypochlorite and an excess of sodium hydroxide and intimately mix the sweetened product with the unsweetened hydrocarbon fluid in such proportions that the sweetened product is slightly in excess of the quantity necessary to sweeten the sour hydrocarbon fluid and yield a completely sweetened composite of the two. We determine by experiment and plant operation the exact Volumes of the hypochlorite-sweetened and the sour hydrocarbon fluids to mix in order to obtain a sweet mixture of the two.

The concentration of sodium hypochlorite and sodium hydroxide in the sodium hypochlorite solution may be varied over a very wide range. Other hypcchlorites, such as calcium hypochlorite, hypochlorous acid, or their equivalents, may also be employed. No claim is made to sweetening solely by these hypochlorites. 7

We do not claim a method of sweetening by diluting a small quantity of sour petroleum hydrocarbon fluid with a large quantity of sweetened fluid to merely decrease the mercaptan content of the mixture beyond a point to 'which the doctor test is sensitive.

We do not claim the utilization of any hypochlorite treating agent which might be entrained in the oil, but claim only the oxidation resulting from the oil solubleoxidizing sulfur compounds.

What we claim and desire to secure by Letters Patent is:

1. A process for improving hypochlorite treated petroleum oil, comprising treating the oil with an alkaline hypochlorite solution, whereby sulfur compounds with oxidizing properties are formed in the oil, separating the oil from the hypochlorite solution, adding a mercaptan to the oil in such quantity that the amount of mercaptan is substantially equivalent to the sulfur compounds with oxidizing properties in said hypochlorite treated oil, whereby the sulfur compounds with oxidizing properties are converted to disulfides, and an improved oil is obtained.

2. A process for improving hypochlorite treated petroleum oil, comprising treating the oil with an alkaline hypochlorite solution whereby sulfur compounds with oxidizing properties are 7 formed in'the oil, separating the oil from the hypochlorite solution, adding a mercaptan-containing petroleum oil to said hypochlorite treated oil in such quantity that the amount of mercaptan is substantially equival nt to the sulfur compounds with oxidizing properties in said hypochlorite treated oil, whereby the mercaptans and said oxidizing sulfur compounds react to form disulfides, and an improved oil is obtained.

3. An improved process for sweetening mercaptan-containing petroleum oil, comprising contacting a portion of the mercaptan-containing oil with an alkaline hypochlorite solution whereby a part of the mercaptans are converted to disulfides and the rest of the mercaptans are converted to sulfurcompounds with oxidizing properties, said sulfur oxidizing compounds remaining in the oil, separating the said treated oil from the hypochlorite solution, and adding mercaptan-containing petroleum oil to the treated oil free of hypochlorite solutionin an amount substantially equivalent to the sulfur oxidizing compounds in the treated oil, whereby the mercaptans and said sulfur oxidizing compounds react to form disulfides, and thereby obtaining an improved sweetened petroleum oil.

4. A process for improving hypochlorite treated petroleum oil, comprising treating the oil with an alkaline hypochlorite solution, whereby sulfur compounds with oxidizing properties are properties are converted to disulfides, and an improved oil is obtained.

5. A process for improving. hypochlorite treated petroleum oil, comprising treating the oil with an alkaline hypochlorite solution whereby sulfur compounds with oxidizing properties are formed in the oil, separating the oil from the hypochlorite solution, adding a mercaptan-containing petroleum oil to said hypochlorite treated oil in such quantity that the amount of mercap tan is substantially equivalent to the sulfur compounds with oxidizing properties in said hypochlorite treated oil, whereby the mercaptans and said oxidizing sulfur compounds react to form disulfides, and an oil substantially non-corrosive to the sunlight copper strip is obtained.

6. A process for improving hypochlorite treated petroleum oil, comprising treating the oil with an alkaline hypochlorite solution whereby sulfur compounds with oxidizing properties are formed in the oil, separating the oil from the hypochlorite solution, adding a mercaptan-containing petroleum oil to said hypochlorite treated oil in such quantity that the amount of mercap-' tan is substantialy equivalent to the sulfur comseparating the said treated oil from the hypo- 7 chlorite solution, and adding mercaptan-containing petroleum oil to the'treated oil free of hypochlorite solution in an amount substantially equivalent to the sulfur oxidizing compounds in the treated oil, wherebythe mercaptans and said sulfur oxidizing compounds react to form disulfides, and a sweetened petroleum oil isobtained which is substantially free from corrosive substances and is substantially stable to sunlight. T

8. A process for improving petroleum oilcontaining sulfur compounds with oxidizing properties, such compounds having been formed during the sweetening of said oil with an alkaline hypo"- chloritersolution, comprising adding a mercaptan to the oil while out of contact with the hypochlorite solution, whereby the sulfur compounds with oxidizing properties are converted to disulfides, and an improved oil is obtained.

WALTER A. SCHULZE. LOVELL V. CHANEY. 

